Well, the tuner matches what's in front of it to what is behind it. with
the new technology and moisture proof boxes, its worth considering, since
having the tuner at the base of the antenna should transfer the most power
to the radiator, instead of the radiator and coax. I doubt if this would
work for a balanced fed antenna.
The QRP folks here may have better info on this idea.
I don't think that their are high power remote tuners, but 100 watts can be
done.